In the related art, a seatbelt apparatus attached to a vehicle seat of a vehicle or the like prevents an occupant from jerking forward from the seat by constraining the occupant with a seatbelt in the case of an emergency such as a case where large deceleration is applied on the vehicle at the time of a collision or the like.
In general, such a seatbelt apparatus includes a seatbelt retractor. Examples of such a seatbelt retractor generally include an emergency locking seatbelt retractor (ELR) configured to prevent a withdrawal of the seatbelt by locking the rotation of a spool in a seatbelt withdrawing direction in the case of an emergency such as that described above and an automatic locking seatbelt retractor (ALR) having the function of the ELR and configured to prevent the withdrawal of the seatbelt by locking the rotation of the spool in the seatbelt withdrawing direction during the course of retraction of the seatbelt after the entire amount of the seatbelt has retracted until a predetermined amount of the seatbelt is retracted. The ALR includes an ELR-ALR switching mechanism configured to switch between the function of the ELR and the function of the ALR.
The seatbelt retractor in the related art is provided with a seatbelt withdrawal sensor (a so-called webbing sensor) configured to prevent the withdrawal of the seatbelt by the rocking movement when the seatbelt is abruptly withdrawn at a speed faster than a normal seatbelt withdrawing speed (that is, a withdrawing acceleration larger than a normal withdrawing acceleration when the seatbelt is fastened) in many cases. The seatbelt withdrawal sensor may prevent the withdrawal of the seatbelt through a rocking movement also when the entire amount of the withdrawn seatbelt is retracted. In other words, there is a case where normal withdrawal of the seatbelt becomes difficult due to the seatbelt withdrawal sensor making a rocking movement upon the entire amount of the seatbelt being retracted, that is, a so called end locking occurs.
Accordingly, there is proposed a seatbelt retractor that is capable of preventing end locking caused by a seatbelt withdrawal sensor (for example, see Patent Literature 1 and 2). The seatbelt retractor described in Patent Literatures 1 and 2 are provided with a cam plate configured to rotate in conjunction with a spool that winds a seatbelt, and the cam plate is provided with a helical long cam groove. The seatbelt retractor is provided with a rocking movement prevention member configured to prevent the rocking movement of the seatbelt withdrawal sensor provided so as to be rotatable while being controlled by the above-described cam groove.
Then, the cam plate rotates in the seatbelt withdrawing direction upon withdrawal of the seatbelt that has been retracted entirely, and the seatbelt is withdrawn by a predetermined amount, so that the rocking movement prevention member rotates toward a freely rocking position where the rocking movement prevention member allows the seatbelt withdrawal sensor to freely rock through control by the cam groove of the cam plate. Also, upon rotation of the cam plate in a seatbelt retracting direction caused by the retraction of the withdrawn seatbelt, the rocking movement prevention member rotates toward a rocking movement prevention position at which the rocking movement prevention member prevents the rocking movement of the seatbelt withdrawal sensor while being controlled by the cam groove. Then, when retracting the withdrawn seatbelt entirely, since the rocking movement prevention member is set to the rocking movement prevention position, the seatbelt withdrawal sensor cannot rock and hence end locking is prevented.
In the seatbelt retractor described in Patent Literatures 1 and 2 described above, the rotation of the rocking movement prevention member is controlled by the cam groove of the cam plate. In such a case, while the amount of rotation of the spool is relatively large, the amount of rotation of the rocking movement prevention member between the freely rocking position and the rocking movement prevention position is relatively small. Therefore, the cam groove has to be relatively long. However, when the cam groove is long, the outer diameter of the cam plate needs to be correspondingly larger in order to secure a space for forming the cam groove. Therefore, the seatbelt retractor becomes inevitably large.
Accordingly, there is proposed a seatbelt retractor that has a smaller and more compact structure for preventing end locking and that is capable of preventing end locking caused by the seatbelt withdrawal sensor effectively (for example, see Patent Literature 3). In the seatbelt retractor described in Patent Literature 3, a pair of stoppers serving as a rocking movement prevention member move in the radial direction passing through the center of rotation of the spool along a guide groove of an eccentric gear of the ELR-ALR switching mechanism while being controlled by a cam groove provided on a case at the time of rotation of the eccentric gear in association with retraction and withdrawal of the seatbelt. Then, when the seatbelt is retracted substantially entirely, the pair of stoppers prevent the rocking movement of a flywheel by pressing an inner peripheral surface of a ring portion provided on the flywheel as the seatbelt withdrawal sensor by being positioned in a large-diameter-side arcuate-shaped groove of the cam groove. When the seatbelt is withdrawn by a predetermined amount from the state of being entirely retracted, the stoppers are positioned in a small-diameter-side arcuate-shaped groove and hence do not press the inner peripheral surface of the ring portion thus allowing the flywheel to freely rock. In the seatbelt retractor described in Patent Literature 3, end locking caused by the belt withdrawal sensor may be prevented with a simple configuration using the rocking movement prevention member that moves in the direction of the diameter of the spool.